Rack::Utils#normalize_params should be ignorant of the provided param…

…s class.

lib/rack/utils.rb

@@ -111,21 +111,26 @@ def normalize_params(params, name, v = nil)
         child_key = $1
         params[k] ||= []
         raise TypeError, "expected Array (got #{params[k].class.name}) for param `#{k}'" unless params[k].is_a?(Array)
-        if params[k].last.is_a?(KeySpaceConstrainedParams) && !params[k].last.key?(child_key)
+        if params_hash_type?(params[k].last) && !params[k].last.key?(child_key)
           normalize_params(params[k].last, child_key, v)
         else
-          params[k] << normalize_params(KeySpaceConstrainedParams.new, child_key, v)
+          params[k] << normalize_params(params.class.new, child_key, v)
         end
       else
-        params[k] ||= KeySpaceConstrainedParams.new
-        raise TypeError, "expected Hash (got #{params[k].class.name}) for param `#{k}'" unless params[k].is_a?(KeySpaceConstrainedParams)
+        params[k] ||= params.class.new
+        raise TypeError, "expected Hash (got #{params[k].class.name}) for param `#{k}'" unless params_hash_type?(params[k])
         params[k] = normalize_params(params[k], after, v)
       end
 
       return params
     end
     module_function :normalize_params
 
+    def params_hash_type?(obj)
+      obj.kind_of?(KeySpaceConstrainedParams) || obj.kind_of?(Hash)
+    end
+    module_function :params_hash_type?
+
     def build_query(params)
       params.map { |k, v|
         if v.class == Array